I´m performing fmri. There is a persistent high signal on the occiptal region even using prescan normalize. When we analyze the data, all higher Z-scores are on this region, a d the paradigm does not justify it. How can I manage this? the 3 options of prescan normalize change this effect? Thanks in advanced!
Hi Lian,
the high signal in the occipital region is due to surface coil or to be more precise: due to the fact that back of the subjects head lies on the coil (therefore is very close to the receiving coil). The purpose of "prescan normalize" is exactly to prevent or minimize this effect. Therefore you could use this option (normal mode should be fine).
Another option is to use a thicker cushion to raise the subjects head (and thereby achieve similar distances to all parts of the coil + more comfort for your subjects).
Nevertheless it's astonishing that you report systematically raised Z-scores in this region: by theory Z-scores should be independent of the magnitude of the signal because mainly (normalized) differences should influence the Z-scores. Probably increased SNR by the increased signal could be an explanation but this effect is not very strong.
Halo Juergen,
Thanks for your reply. We are testing different kinds of cushions to get a better performance.
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